Major sources of renewable energy, wind and solar, are weather- and time-dependent. Furthermore, the geographic areas best suited for harvesting these resources are remote. Therefore, chemical energy storage/transportation is viewed as the most probable way of harvesting the renewable energy.
Alternative chemical energy sources may include hydrocarbons and oxygenated aliphatics, synthesized from CO and H2 via for example the Fischer-Tropsch process. More recently, the Fischer-Tropsch process has been viewed as a viable method for preparing even heavier hydrocarbons such as diesel fuels, and more preferably waxy molecules for conversion to clean, efficient lubricants. The energy and raw materials for this are currently derived from the burning of coal, with the accompanying release of CO2 as a by-product. However, such process increases the CO2 in the atmosphere and may lead to serious global climate. Alternatively, CO2 itself may be used as a source of carbon for the production of petroleum-like materials. This may then lead to the possibility of regulating the concentration of atmospheric CO2.
As CO2 is one of the most thermodynamically stable carbon compounds, a highly energetic reductant or an external source of energy is required to convert it into other carbon compounds. It is well known that carbonates (CO32−) can be reduced electrochemically according to the following:CO32−+2e−→CO+2O2−  Cathode (1)2O−−2e−→O2  Anode (2)However several side products can yield elementary carbon on the cathode or CO2 on the anode:Cathode: CO32−+4e−→C+3O2−or on the anode: CO32−−2e−→CO2+½O2 Furthermore the produced CO may decompose:COCO2+C
Methanol is one of the major chemical raw materials, ranking third in volume behind ammonia and ethylene. Worldwide demand for methanol as a chemical raw material continues to rise especially in view of its increasingly important role (along with dimethyl ether) as a source of olefins such as ethylene and propylene and as an alternative energy source, for example, as a motor fuel additive or in the conversion of methanol to gasoline.
Methanol is not only a convenient and safe way to store energy, but, together with its derived dimethyl ether (DME), is an excellent fuel. Dimethyl ether is easily obtained from methanol by dehydration and is an effective fuel particularly in diesel engines because of its high octane number and favorable properties. Methanol and dimethyl ether can be blended with gasoline or diesel and used as fuels, for example in internal combustion engines or electricity generators. One of the most efficient uses of methanol is in fuel cells, particularly in direct methanol fuel cell (DMFC), in which methanol is directly oxidized with air to carbon dioxide and water while producing electricity.
Thus, there is a need for an efficient electrochemical method and an efficient electrochemical cell for the reduction of carbonate to carbon monoxide (CO), which further can yield chemical energy sources, such as for example, methanol. Further, the production of CO can be used for energy transportation.